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E39 (1997 - 2003) The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

I think that a lot of confusion on this issue stems from the fact that it`s often not made clear whether we`re discussing the K&N replacement (panel-type) filter element (to be used in the stock airbox), or the complete K&N CAI system, where the stock airbox has been eliminated.
A couple of E46 Forum members have done dyno runs which showed as much as a 3 HP drop when the K&N CAI system was used (compared to stock), and even luminaries such as Steve Dinan himself admitted that his CAI provided no noticeable gain over the stock unit. Given the fact that BMW MAFs have proven to be rather sensitive *under normal conditions*, I fail to see any logical reason to introduce yet ANOTHER potential trouble spot (an oiled element) into the mix.
Sometimes you`re better off leaving well-enough alone....

K&N here for the past 45K miles - no problemos. I wash and oil it every summer though

ive yet to see an E39 with a faulty motor caused by a K&N filter and I know about half of dozen of them with 1 528 having ~170K miles on it. My MAFs been fine too, no complaints there either.

OP, your best bet is to take everything with a grain of salt, I know for a fact some people here know a little too much for their own good that they complicate the decision making of other even when it comes to simple things

While I agree that things can get a little too complicated on this board, but on this subject of stock vs K&N, realize that if there was ANY gain in performace (HP, MPG, etc....)--no matter how small said gain is--don't you think EVERY person on this board would have it installed on their car by now? Especially considering the relatively low $70 price tag.....

I've used a K&N filter for over 100k Miles. No problems. Not saying some have had issues, but I haven't. I've also took the air horn out of my airbox. I think there is a slight positive performance difference, but I think that's due to the dinan stage one engine software.

No I haven't. I run full synthetic in all my cars, and I always change the oil in the E39 about every 3-5k miles... usually closer to 5k. How much does it cost to have my oil analyzed? I'm due for oil change right about now- so I'm guessing now would be the time to have it analyzed.

Couldn't hurt. Last I checked, an oil analysis was around $25.00 from Blackstone Labs

We here in the northeast have to deal with A LOT of sand due to its use as a traction aid in winter and the residue that hangs around all year, gradually being ground into finer and finer particles. I see it in my engine compartment all the time and have to constantly vacuum it out of there. Side windows get scratched and windshields are sandblasted so it's not too far of a stretch to believe my air intake sees quite a lot of fine mesh silicate minerals.

there isdubious unscientific evidence that k7n does not filter as well as oem paper, what never gets mentioned of course is that k7n removes like 99.5 % of the material in the air stream(and what also doesnt get mentioned is that this only applies when freshly oiled, after a short time the filtration effectiveness increases as the filter gets a little dirty.) so the three times better number is totally stupid because it means that the best fitler filters 99.7 % or 99.8 % of material, to here the yes men tell it its as if the K&N only filters 1/3 of the material in the airstream.

the other undiscussed benefit lies in the fact that K&Ns take a long time to get dirty enough to restrict air flow in any meaningful way where as a few days of driving in dusty conditions can rapidly degrade the flow capacity of a paper element filter. there is no question that fresh paper filters filter better than K&N and that they have similar flow rates. but it is what happens after a thousand miles that makes all the difference in the world.

Well I've tried K&N oiled filters in my car which is a 2004 V8 Toyota Tundra (the X3 i post about here is my wife's which of course I maintain) and have never seen any real MPG or performance gains. Whatever the stated "scientific" gains may be they rarely are accompanied by one very important piece of information which is "what RPM range are those gains being realized at"? They are probably very high RPM ranges, ie: when you're seriously on the gas ... not an RPM range that you are driving in 90% of the time so you'll likely not see any real difference.

As for filtration, here's a little common sense test ... take your K&N and hold it up to a light and lo and behold you will see daylight shining through tiny little holes. That is not trapping micro particles and even if the difference between a K&N and good synthetic or paper disposable is only .5% over time that will add up to a lot more dirt in your engine. If you want your car to last as long as possible then forget the K&N in my opinion.

Here is a little tutorial for anyone wanting to change their own engine air filter but maybe never has before, it's overkill but I wanted it to be simple for a first timer:

It's very simple, any filter media that lets more air in also lets more dirt in. In order to allow a free flowing filter in must either be more porous (allowing more and larger dirt particles) or have a larger filter surface area and the K&N does not have more folds and surface area than OEM.

I recently purchased a 2004 330 CI with a K&N cold air intake. After about 200 miles of interstate driving the on the way home the SES light popped on. P2227, P0171, P0174.
Any advice would be appreciated

Quote:

Originally Posted by Fast Bob

K&Ns on BMWs are bad JuJu....they tend to blow out the MAF. Converting back to the stock configuration ASAP is your best bet. Besides, stock is more efficient (!) than the K&N....

Get a can of CRC MAF cleaner and spray yours down....be careful, it`s quite fragile inside.